复杂动态系统理论自上个世纪末被引入应用语言学领域后，有不少研究对二语学习者句法复杂度的动态发展进行了研究。但目前，多数研究的研究对象为较高水平的学习者，如大学生和研究生，针对中低水平学习者的研究相对较少。本研究以动态系统理论为框架，对四名高一学生在一学期内的作文的句法复杂度发展以及内部指标间的交互进行了追踪和分析，详细描述并讨论了每个学生在一学期内句法复杂性的四个维度（T单元的平均长度（MLT）、每T单元中从句的数量（C/T）、每从句中并列短语的数量（CP/C）、每T单元中复合名词短语的数量（CN/T））上的具体发展过程，以及四个内部指标间的动态关系。作文样本来自于学生每周提交的读书心得。样本由L2语法复杂性分析器（L2SCA）进行初步分析处理后借助数据可视化工具（移动极值图、移动相关图）和变点分析进行进一步探究。

研究结果显示，每一个指标都呈现非线性和不规则的发展模式，在进步的过程中也常常伴随着退步。四位学习者的句法复杂度指标在一个学期之后均有增长，但增长幅度和发展路径均有所不同。虽然一个学习者的句法复杂度指标可能在某一时刻表现出高度的可变性，但同一个指标在另一个学习者身上可能表现出稳定性。此外，个体参与者的成长路径与群体的不同。具体表现为，在某些情况下，个体轨迹发展保持稳定，而群体平均值呈现上升趋势和波动。

此外，研究结果还表明，在大多数学习者中，有两对指标是正相关的，即每T单元中从句的数量与T单元的平均长度和每T单元中复合名词短语的数量与T单元的平均长度。此外，发展过程中也存在内部指标之间的竞争关系，如每T单元中从句的数量与每从句中并列短语的数量。一个指标的发展可能有助于另一个指标同时发展，也可能会起暂时的阻碍作用。研究还显示，无论是正相关还是负相关都不是恒定的，而是会随着时间而波动。

Since the introduction of the dynamic system theory in applied linguistics at the end of the last century, many studies examined the dynamic development of syntactic complexity in second language learners. At present, most of the research topics pertain to higher-level learners including college students and graduate students, and relatively few studies focus on middle- and low-level learners. Based on the framework of dynamic system theory, this study tracks and analyzes the development of syntactic complexity of writings and the interaction between its internal indices of 4 senior high school students in one semester. It was discussed in detail the specific development process of each student on the four dimensions of syntactic complexity (i.e., mean length of T-units (MLT), clauses per T-unit (C/T), coordinate phrases per clause (CP/C), and complex nominals per T-unit (CN/T)), as well as the dynamic relationship between the four indices. The writings sample comes from the reading reflection submitted by students every week. The samples are preliminarily analyzed and processed by L2 syntactic complexity analyzer (L2SCA), and then further examined with the help of data visualization tools (moving min-max graph, moving correlation graph) and change point analysis.

The results reveal that a non-linear and irregular pattern of development is displayed by all the indices, as regression usually accompanies progression. All four learners’ syntactic complexity indices increased after one semester, but the magnitude of the increase and the path of development differs. While one learner’s syntactic complexity index showed a high degree of variability in one moment, that of another learner exhibited stability. Moreover, the growth paths of individual participants differed from those of the group. Specifically, in certain cases, individual trajectory development remained stable, while group averages exhibited upward trends and fluctuations.

The study also finds out that there are two pairs of indices that are positively correlated in most learners, namely clauses per T-unit and mean length of T-units as well as complex nominals per T-unit and mean length of T-units. And a negative correlation was presented as well, such as between clauses per T-unit and coordinate phrases per clause. The development of one index might help another index improve, or it might hinder it temporarily. It has also been shown that all of these correlations, whether positive or negative, were not constant but fluctuate with time.